The polyarylene sulfide typified by polyphenylene sulfide (may be abbreviated as PPS hereinafter) is a resin having properties suitable as engineering plastics, such as excellent heat resistance, barrier property, chemical resistance, electrical resistance property, moist heat resistance and flame resistance. The polyarylene sulfide resin can be molded into various kinds of molded components, films, sheets, fibers and so on by injection molding and extrusion molding, and are widely used in fields where heat resistance and chemical resistance are required, such as those of various kinds of electric and electronic components, mechanical components and automobile components.
However, the polyarylene sulfide resin has the disadvantage of poor toughness while having the above-mentioned properties. A method has been disclosed in which a metal is dispersed in a polyarylene sulfide resin for the purpose of improving toughness. For improvement of toughness, the area of contact between the polyarylene sulfide resin and the metal is preferably large, and thus the metal particles are desired to have a large surface area per mass, i.e. a small particle size.
For example, Patent Document 1 discloses a method for producing a polyarylene sulfide composite material in which an inorganic metal salt is dissolved in a solvent, the resulting solution is mixed with a polyarylene sulfide, the solvent is then removed, and the resulting solid solution or mixture including the polyarylene sulfide and the metal salt is melt-kneaded to reduce the inorganic metal salt to a metal and disperse the metal in the polyarylene sulfide as particles having an average particle size of 0.5 to 30 nm.
Patent Document 2 discloses a plastic composition in which metal fibers of iron, nickel or an iron alloy and a metal powder are filled into and dispersed in a thermoplastic resin for the purpose of imparting conductivity.
Patent Document 3 discloses a resin composition including metal ultrafine particles, or a molded product thereof, and a method for producing the same, the resin composition being produced by heating and molding a mixture of a metal oxide or a metal organic compound and a resin at a temperature equal to or higher than the thermal decomposition initiating temperature of the metal oxide or metal compound and lower than the degradation temperature of the resin to generate metal ultrafine particles having an average particle size of 1 to 100 nm.
Patent Document 4 discloses a method for producing a polyarylene sulfide resin composition with metal element-containing nanoparticles dispersed therein in which a polyarylene sulfide resin and an organic metal compound are dissolved in an organic solvent capable of dissolving a polyarylene sulfide resin, and then precipitated, and Patent Document 5 discloses a method for producing a composite of a polyarylene sulfide resin and inorganic fine particles in which from an organic solvent solution with a polyarylene sulfide resin dissolved and inorganic fine particles dispersed therein, the polyarylene sulfide resin is precipitated. By either of these methods, a polyarylene sulfide resin composition can be produced without performing melt kneading.
As a specific method for producing a polyarylene sulfide, a method has been proposed in which an alkali metal sulfide such as sodium sulfide is reacted with a polyhalogenated aromatic compound such as p-dichlorobenzene in an organic amide solvent such as N-methyl-2-pyrrolidone, and this method is widely used as a method for industrially producing a polyarylene sulfide (e.g. Patent Document 6). However, this production method is a high-energy consumption type which requires carrying out a reaction at a high temperature and a high pressure and under strong alkali conditions, needs an expensive high-boiling-point polar solvent such as N-methyl-2-pyrrolidone, and takes much costs for recovery of the solvent, so that much process costs are required. Further, since a high-boiling-point solvent is used, a solvent-derived gas tends to be easily generated at the time of heating the resulting polyarylene sulfide.
As another method for producing a polyarylene sulfide, which is intended to solve the problems of the methods for producing a polyarylene sulfide as described above, a method for producing a polyarylene sulfide has been disclosed in which a cyclic polyarylene sulfide is heated (e.g. Patent Document 7).
A method for polymerizing polyphenylene sulfide is also known in which a mixture of cyclic polyphenylene sulfide and linear polyphenylene sulfide as a monomer source is heated (Non-Patent Document 1).
As a method for accelerating conversion in conversion of a cyclic polyarylene sulfide to a polyarylene sulfide, a method using various kinds of catalyst components (compound effective to generate radicals, ionic compound, organic carboxylic acid, etc.) is known.
Patent Document 8 and Non-Patent Document 2 each disclose, for example, a compound which generates sulfur radicals when heated, as a compound effective to generate radicals. Specifically, a compound containing a disulfide bond is disclosed.
Patent Documents 9 and 10 each disclose an ionic compound that may serve as a ring-opening polymerization catalyst in anionic polymerization. Specifically, for example, a method using an alkali metal salt of sulfur which generates an anion species such as a sodium thiophenolate is disclosed.
Patent Document 11 discloses a method in which an ionic compound that may serve as a ring-opening polymerization catalyst in anionic polymerization and a Lewis acid are made to coexist. Specifically, a method is disclosed in which a sodium thiophenolate and copper chloride (II) are made to coexist.
A method using a transition metal compound (zero-valent transition metal compound or low-valent iron compound) as a catalyst for accelerating conversion in conversion of a cyclic polyarylene sulfide to a polyarylene sulfide is also known (e.g. Patent Documents 12 and 13).
Specifically, Patent Document 12 discloses a method using, for example, tetrakis(triphenylphosphine) palladium, tetrakis(triphenylphosphine) nickel, or the like as a zero-valent transition metal compound.
Specifically, Patent Document 13 discloses a method using, for example, iron chloride as a low-valent iron compound.
Patent Document 14 discloses a method using a carbanion as an initiator. Specifically, a method using, for example, a sodium 4-chlorophenylacetate or 4-chlorophenylacetic acid is disclosed.